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We are not alone.

There are likely "tens of billions" of Earth-like planets in our Milky Way galaxy, according to a study released Monday by astronomers from the University of California-Berkeley and the University of Hawaii.

"Planets like our Earth are relatively common throughout the Milky Way galaxy," said astronomer Andrew Howard of the University of Hawaii.

In fact, the nearest Earth-like planet may be "only" 12 light years away, which is roughly 72 trillion miles.

Overall, astronomers now estimate that about one in five sun-like stars have planets that are nearly the size of Earth and also have a surface temperature conducive to the development of life.

Like Goldilocks tasting the porridge, temperatures must be "just right" for life to develop: Planets must have a so-called "habitable zone" with "lukewarm temperatures, so that water would not be frozen into ice or vaporized into steam but instead remain a liquid, because liquid water is now understood to be the prerequisite for life," said Geoffrey Marcy, a professor of astronomy at Berkeley.

The discovery was based on the most accurate statistical analysis yet of all the observations from the Kepler telescope, a space observatory launched in 2009 specifically designed to locate planets around other stars.

The research was based mainly on an exhaustive, three-year search of Kepler data undertaken by Erik Petigura, a graduate student at the University of California, Berkeley.

"Now, for the first time, humanity has a measure of how common Earth-size planets are around sun-like stars," he added.

Howard estimated that our galaxy has 40 billion planets "for life to get started and to evolve."

And going beyond our galaxy, Marcy reminds us that the Milky Way is just a typical galaxy within our universe, which contains hundreds of billions of galaxies, each of which is similar to our Milky Way.

"With tens of billions of Earth-like planets in each galaxy, our entire universe must contain billions of billions of Earth-like planets," Marcy said

The study was published online Monday in the Proceedings of the National Academy of Sciences using data from the Kepler telescope. The $591 million Kepler telescope is now crippled and nearing the end of its four-year mission

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